Breastfeeding induces a different metabolic and endocrine response than feeding conventional infant formula, and it has also been associated with slower weight gain and reduced disease risk in later life. The underlying programming mechanisms remain to be explored. Breastfeeding has been reported to induce lower levels of insulin, insulin-like growth factor-1 and some amino acids (AAs) than formula feeding. In the Childhood Obesity Project (CHOP), infants fed a conventional protein-rich formula had a higher BMI at 2 and 6 years than those fed a protein-reduced formula. At 6 months, higher protein intakes induced increased plasma concentrations of branched-chain AAs (BCAAs) and their oxidation products, short-chain acylcarnitines. With increasing BCAA levels, these short-chain acylcarnitines increased proportionally only until a break point was reached, after which BCAAs seemed to escape their degradation. The resulting marked elevation in BCAA levels with high-protein (HP) intakes appears to contribute to increased insulin levels and to affect β-oxidation of fatty acids. The ratios of long-chain acylcarnitines to free carnitine decreased in infants who received a HP formula, which indicates a reduced initiation of β-oxidation. We conclude that HP intakes inducing high BCAA plasma levels may inhibit fat oxidation and thereby enhance body fat deposition and adiposity.
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